The product is an expansion for Arkham Horror: The Card Game. There is no option to play separately with only the add-on, the main game is required.
The Unspeakable Oath is the second expansion in the Path to Carcosa cycle for Arkham Horror: The Card Game.
The Unspeakable Oath will continue your investigation, which will take you to Arkham Asylum, and although you will be surrounded by lunatics, locked doors and the unknown, you will have to look for clues about dark forces. Try not to miss these and learn from your mistakes and maybe you will find helpers in your difficult mission.